For commercialization, many objects and products are packaged in prefabricated trays and sealed with a so-called stretch film. In these cases, a stretchable and in most cases transparent film is wrapped around the tray to fasten the content and to protect it from external influences. Since no hermetical closing-in of the content results, the atmospheric oxygen can adversely affect perishable products. However, the packages are optically very attractive, particularly if food such as meat products protrudes above the edge of the tray and appear very vivid in combination with the transparent cover.
In vacuum packages or so-called atmos-packages, the acting of atmospheric oxygen on perishable food is prevented by hermetical sealing. To achieve this, an impermeable film is sealed onto the tray as a cover after drawing off the air from it by evacuating and possibly substituting it by an inert gas.
If conventional tray sealing machines are used, the content of the package must not protrude above the upper edge of the tray when using a planar covering film, since else the covering film may form creases and during sealing untight spots arise in the sealing seam.
From U.S. Pat. No. 6,408,598 a method for manufacturing such a package is known. A proposal is made to deform a covering film which was heated in a heated cavity above the product. In doing so, the risk is given that creases arise in the peripheral region causing leakages in the sealing region. Additionally, the heating of the covering film before and during deformation is disadvantageous since shrinkable films loose their shrinking property at higher temperatures.
From EP-A-1 038 773 a packaging machine comprising a schematically indicated closing station and an apparatus for feeding trays to be closed by an upper film into the closing station and conveying them out, respectively, is known. In particular, in the known packaging machines such closing stations are implemented to be evacuating and sealing stations.
It is object of the present invention to avoid the above disadvantages in a method for packaging and in a packaging machine, respectively, and to provide a method and a device which allows reliable manufacturing of a package comprising a tray and a product protruding above the edge of the tray. The such-formed product packages shall be impermeable as well as allow for an advantageous presentation under optical aspects.
This object is solved by the method specified in claim 1 and by the packaging machine specified in the two parallel claims 3 and 5.
Further developments of the invention are specified in the subordinate claims, respectively.